If the Earth were a globe, it would, if we take Valentia to be the place of departure, curvate downwards, in the 1665 miles across the Atlantic to Newfoundland, according to the astronomers' own tables, more than three hundred miles; but, as the surface of the Atlantic does not do so - the fact of its levelness having been clearly demonstrated by Telegraph Cable surveyors, - it follows that we have a grand proof that Earth is not a globe.
11.) As the mariners' compass points north and south at one time, and as the North, to which it is attracted is that part of the Earth situated where the North Star is in the zenith, it follows that there is no south "point" or "pole" but that, while the centre is North, a vast circumference must be South in its whole extent. This is a proof that the Earth is not a globe.
That the mariners' compass points north and south at the same time is a fact as indisputable as that two and two makes four; but that this would be impossible if the thing, were placed on a globe with "north" and "south' at the centre of opposite hemispheres is a fact that does not figure in the school-books, though very easily seen: and it requires no lengthy train of reasoning to bring out of it a pointed proof that the Earth is not a globe.

Astronomers tell us that, in consequence of the Earth's "rotundity," the perpendicular walls of buildings are, nowhere, parallel, and that even the walls of houses on opposite sides of a street are not! But, since all observation fails to find any evidence of this want of parallelism which theory demands, the idea must be renounced as being absurd and in opposition to all well-known facts. This is a proof that the Earth is not a globe.

In 1956, Samuel Shenton created a more modern version of the Flat Earth Society, to collect a variety of followers of Rowbowtham's experiments. When the first images of the earth taken from space were released, Shenton claimed that they were false. In the 1970s and 1980s, they released a newsletter called the Flat Earth News, which often debated NASA and other space agencies.

155) Some people claim to have seen the curvature of the Earth out their airplane windows. The glass used in all commercial airplanes, however, is curved to remain flush with the fuselage. This creates a slight effect mixed with confirmation bias people mistake for being the alleged curvature of the Earth. In actuality, the fact that you can see the horizon at eye-level at 35,000 feet out both port/starboard windows proves the Earth is flat. If the Earth were a ball, no matter how big, the horizon would stay exactly where it was and you would have to look DOWN further and further to see the horizon at all. Looking straight out the window at 35,000 feet you should see nothing but "outer-space" from the port and starboard windows, as the Earth/horizon are supposed to be BELOW you. If they are visible at eye level outside both side windows, it’s because the Earth is flat!
As previously mentioned, the reaction of bodies of water with sunlight is very different from that of land. Being largely transparent, light penetrates deeply into water, so that the sun’s light is absorbed throughout a thick layer from the surface to some depth rather than just on the surface, as with land. Additionally, water has a high specific heat, which means that its temperature increases very slowly as heat is added. Consequently, water exposed to sunlight does not change temperature appreciably throughout the day, so there is no heating of air in contact with the water. If anything, during summer afternoons, when land is rapidly heating, bodies of water frequently are cooler than air temperature. The cooler water chills the air in direct contact with it, so the air lying just above water often is cooler than air higher up. Since air temperature normally decreases with height, this temperature reversal from the norm is called a temperature inversion. Temperature inversions are common over bodies of water during late spring and into summer. Since this temperature structure is the reverse of what causes inferior mirages, inferior mirages are far less commonly noticed over water. This happens particularly during the summer, when inferior mirages are common over land.

78) From Anchorage, Alaska at an elevation of 102 feet, on clear days Mount Foraker can be seen with the naked eye 120 miles away. If Earth were a ball 25,000 miles in circumference, Mount Foraker’s 17,400 summit should be leaning back away from the observer covered by 7,719 feet of curved Earth. In reality, however, the entire mountain can be quite easily seen standing straight from base to summit.